Hi, I have a 2003 Audi A8 with dual fuel pumps in the rear. The vehicle initially would start fine then would ocassionally fail and misfire, then it got worse and worse. It has 60,000km on clock and finally got it to do it and hooked on fuel pressure gauge which showed pressure dropping when failing.
Checked pressure reg (all good). When you shut it down and restart it would come right (AT LEAST FOR 1 MIN). Had power to one pump constantly and other for only 40sec to 1 min (on crank). Audi Mechanic told me he thinks both should have constant supply (Not sure).
I thought initially that it may only use one pump and other only worked to equalise tank and initially prime fuel line, thus I replaced pump that was constant due to the thought it was polling out (still the same). I have a diagram for a S6 with a 4.2L motor (same) which only shows the wiring for one pump. It appears it only relies on the Fuel pump relay. Does anyone no if this is the case and if they would follow the same path without entering different relays etc. If it helps they are both the same colours
Any input would be greatly appreciated